两相流检测ECT高速数据采集系统的研制

Design of ECT high speed data acquisition system for two-phase flow measurement

针对电容层析成像系统难以解决的提高数据采集速度与降低噪声之间的矛盾以及抗杂散电容干扰等问题 ,基于电荷放大原理 ,研制了一种高速电容数据采集电路 .与充放电及交流法原理电路相比 ,在一个测量周期内 ,只需一次充放电即可完成对电容的测量 ,不产生脉动噪声 ,故无需滤波器 ,易于数据采集速度的提高 .同时采用了并行测量方式、高速芯片和高速通讯等优化措施 .经测定对 12电极电容传感器的数据采集速度可达 6 0 0幅 /s.对杂散电容具有较强的抑制能力 ,系统灵敏度为 4 .8V/p F,可分辨的最小电容变化量为 0 .5 f F,满足工业实用化要求 .

The filter in Electrical Capacitance Topography (ECT) system is a bottleneck which hampers the increase of sampling speed. Based on the charge amplification principle, a new ECT data acquisition circuit without filter was developed for two-phase flow measurement. This circuit has good stray-immunity for measuring small capacitance. It charges and discharges the detection capacitance only once during one measurement cycle. Compared with charge/discharge and AC-based circuit, this circuit doesn't need filter because there is no pulsating noise. Optimization step of parallel measurement, high speed CMOS chip and fast communication were adopted. Test results showed that the sensitivity of 4.8 V/pF, the resolution of 0.5 fF and the data capture rate of 600 frames/s can be achieved. It satisfies the requirements for industrial online operation.